This invention relates generally to Magneto-Rheological (MR) devices and more particularly to an improved design for an MR damping device.
Devices for suspending parts and controlling or damping their movement relative to one another, are known in the art. For example, such devices are known and used in the automotive field in vehicle suspension systems. The devices might take the form of shocks, struts and other motion or vibration damping devices.
Generally, many such devices utilize fluids for controlling the relative movement of the mechanical parts. For example, hydraulic fluid may be utilized as a medium for creating damping forces or torques or controlling motion, shock and vibrations. One class of such movement control devices utilizes a fluid medium which has characteristics which are controllable through the use of magnetic fields and/or magnetic flux. Such magnetically controlled fluid is referred to as magneto-rheological, or MR, fluid and is comprised of small, soft magnetic particles dispersed within a liquid carrier. The particles are often generally round, and the suitable liquid carrier fluids include hydraulic oils and the like for suspending the particles. MR fluids exhibit a thickening behavior (a rheology change), often referred to as xe2x80x9capparent viscosity change,xe2x80x9d upon being exposed to magnetic fields of sufficient strength. The higher the magnetic field strength to which the MR fluid is exposed, the higher the flow restriction or damping force that can be achieved in the MR device, and vice versa. That is, the flow properties of MR fluids may be selectively altered by magnetic fields.
A typical MR damping device, for example, utilizes an iron core structure disposed within or surrounded by a metal cylinder or casing. MR fluid is positioned to flow between the core and the metal cylinder. The damping effect of the device is due to the relative movement of the core and cylinder with respect to the MR fluid or vice versa. That is, depending upon the use and structure of the MR damping device, the core and cylinder are dynamic and move through the MR fluid or the MR fluid moves between a stationary core and cylinder. To control the damping effects of the device, a magnetic flux is formed in and around the core and the metal cylinder, such that the core and cylinder create a magnetic circuit. The metal cylinder or casing surrounding the core is often referred to as a xe2x80x9cflux ringxe2x80x9d as it directs and provides a path for the magnetic flux which exists in and around the core. Variation of the flux in the device affects the flow of the MR fluid between and around the core and flux ring and thus allows variation of the damping effects of the MR device.
More specifically, during operation of the damping device, the MR fluid flows through a restricted passage or gap formed between the flux ring and the core. Magnetic flux exists within the gap, and therefore, the characteristics of the MR fluid flow through the gap are magnetically controlled by controlling the magnetic flux. By controlling the characteristics of the MR fluid flow, the movement of the core and flux ring relative to the fluid is controlled, thus creating a damping effect to the physical structures which are operably coupled to the MR damping device. To form and vary the magnetic flux in and around the core and within the gap between the core and the flux ring, a magnetic field generator, such as a wire coil is wound around the core. The magnetic flux in the core and in the fluid passage is varied by variation of the electrical current through the coil. The selectively variable magnetic flux dictates the characteristics of the fluid flow in the restricted passage, and the relative movement any mechanical parts and the damping of that movement is then regulated by controlling the characteristics of the fluid flow.
When constructing and assembling a typical MR damping device, as described above, the core and the wire coil which is wound around the core are formed with an insulative material. The material, which may be an insulative plastic material, is molded flush around the coil to protect the coil from the MR fluid. Thereafter, the flux ring, or other metal casing surrounding the core and coil, is placed around the core and coil. Generally, the flux ring is placed concentrically around the core and coil combination to form a fixed annular gap between the flux ring and the core. The MR fluid flows within the gap. As such, it is important to ensure that the gap is generally consistently formed and spaced with respect to the core for uniformity of the damping forces created by the MR damping device. Therefore, the flux ring must be properly located and aligned around the core and coil. In conventional designs of MR damping devices, various fasteners and structures are necessary to provide the proper securement and alignment of the flux ring. For example, non-magnetic hog-rings, needle bearings, and rivets are utilized between the flux ring and the core at three or four positions along the length of the device. Alternatively, two end plates are crimped in place with the flux ring and core for alignment and retention.
While current MR damping devices are suitable to provide the damping forces required, their current design and construction makes them difficult to assemble. Multiple steps are necessary for proper positioning of the elements with respect to each other, particularly with respect to placement of the flux ring. As may be appreciated, multiple steps within a manufacturing and assembly process increase the cost of such a process.
A further drawback to current MR damping device designs is that special fasteners are necessary for locating and aligning the flux ring with respect to the core and coil. Such fastening structures increase the number of parts of the design, providing additional handling and assembly steps and also increasing the cost of the assembly process. Furthermore, using a design with endplates, additional xe2x80x9cdeadxe2x80x9d length occurs along the length of the core and flux ring.
Another particular drawback of the current design is the need for proper location and alignment of the flux ring with respect to the core and coil. It is important that the annular gap has a consistent spacing along the length of the flux ring and core. As may be appreciated, such precise attention to location and alignment of the elements of the MR damping device further increases the assembly steps necessary and thus increases the manufacturing and assembly costs for the device.
The above-mentioned drawbacks of conventional MR damping devices and the manufacture and assembly of same, are further exacerbated by the variations which occur in the assembly due to variations in the various pieces which must be used and aligned. Inconsistency is introduced as a result of batch-to-batch or part-to-part variations of the multiple components which are necessary for construction of the devices. Furthermore, such differences make consistent alignment and location of the components of the device difficult. Of course, all such factors further increase the cost of manufacturing and assembling of the MR damping devices.
Therefore, it is a general objective of this present invention to improve existing MR damping devices, and specifically to improve their design.
It is another objective of the present invention to make such MR damping devices easier and more cost effective to assemble by reducing the assembly steps and also reducing the complexity of such assembly steps.
It is a further objective of the invention to reduce the cost of manufacturing an MR damping device by reducing the number of separate parts which must be handled and utilized in the manufacturing and assembly processes.
It is another objective of the invention to simplify the location and alignment steps associated with certain components of an MR damping device during assembly of such a device.
It is still another objective of the invention to reduce the cost increase in the assembly process which is due to the inconsistencies introduced into such a process by batch-to-batch or part-to-part variations of the multiple necessary components.
These objectives and other objectives are addressed by the present invention which is described in greater detail hereinbelow.
The Magneto-Rheological (MR) damping device of this application addresses the above objectives and utilizes a unique construction for improved performance and enhanced fabrication and manufacturing.
A magneto-rheological (MR) damping device of the invention comprises a core element for carrying a magnetic flux, and a magnetic flux generator, such as a conductive coil, positioned adjacent to a portion of the core element and operable to generate a magnetic flux in the core element. In one embodiment, the conductive coil is wound around the core element. A flux ring surrounds the core element and coil and defines a passage between the flux ring and core element for the flow of an MR fluid. The flux ring is operable for forming a magnetic circuit with the core element and is further operable for confining a portion of the magnetic flux proximate the core element and in the passage.
In accordance with one aspect of the present invention, an insulative sleeve is positioned over the core element and magnetic flux generator to electrically insulate the flux generator from the MR fluid. For example, the sleeve might be press fit over the core element and magnetic flux generator, or might be more loosely positioned. The sleeve includes a plurality of protrusions which extend generally radially outwardly from a center of the core element. The protrusions are configured to engage the flux ring and secure the flux ring in a proper position around the core element and sleeve. More specifically, the protrusions are configured and dimensioned to concentrically align the flux ring with the core element and the center axis of the MR damping device when the flux ring is pressed or placed in position. The protrusions extend radially outwardly generally in equal distances from the center of the core element and are operable to thereby secure the flux ring generally concentrically around the core element and sleeve.
In one embodiment of the invention, the sleeve is molded, such as utilizing a suitable moldable plastic or ceramic, and the protrusions are formed or molded integrally with the sleeve. The protrusions extend longitudinally along a portion of the length of the core element, and may extend generally along the entire length of the core element. Preferably, the protrusions will be positioned annularly around the sleeve in at least three positions for securing and centering the flux ring. For further centering and securing the flux ring, a greater number of protrusions might also be utilized around the sleeve. When the flux ring is pressed or otherwise placed on the core element, the protrusions will hold it in position.
The present invention improves the design of an MR damping device and makes such devices easier and more cost effective to assemble, while reducing the assembly steps and also reducing the complexity of such assembly steps. Furthermore, the number of separate parts which must be handled and utilized during manufacture and assembly is reduced. This reduces inconsistencies based on batch-to-batch or part-to-part variation of such components, and also simplifies the location and alignment steps associated with certain components of the MR damping device during assembly. These advantages and other advantages will become more apparent from the Detailed Description of the invention below.